Environmental perfluoroalkyl acid exposures are associated with liver disease characterized by apoptosis and altered serum adipocytokines

Abstract

Exposures to perfluoroalkyl substances (PFAS) including perfluoroalkyl acids (PFAAs) are associated with increased liver enzymes in cohort studies including the C8 Health Study. In animal models, PFAAs disrupt hepatic lipid metabolism and induce apoptosis to cause nonalcoholic fatty liver disease (NAFLD). PFAAs are immunotoxic and inhibit pro-inflammatory cytokine release from stimulated leukocytes in vitro. This cross-sectional study tests the hypothesis that environmental PFAAs are associated with increased hepatocyte apoptosis and decreased pro-inflammatory cytokines in serum. Biomarkers previously associated with PFAS exposures and/or NAFLD were evaluated as secondary endpoints. Two hundred adult C8 Health Study participants were included. Measured serum biomarkers included: perfluorohexane sulfonate (PFHxS); perfluorooctanoic acid (PFOA); perfluorooctane sulfonate (PFOS); perfluorononanoic acid (PFNA); cytokeratin 18 M30 (CK18 M30, hepatocyte apoptosis); adipocytokines; insulin; and cleaved complement 3 (C3a). Confounder-adjusted linear regression models determined associations between PFAS and disease biomarkers with cut-offs determined by classification and regression tree analysis. CK18 M30 was positively associated with PFHxS (β = 0.889, p = 0.042); PFOA (β = 2.1, p = 0.005); and PFNA (β = 0.567, p = 0.03). Tumor necrosis factor α (TNFα) was inversely associated with PFHxS (β = -0.799, p = 0.001); PFOA (β = - 1.242, p = 0.001); and PFOS (β = -0.704, p < 0.001). Interleukin 8 was inversely associated with PFOS and PFNA. PFAAs were also associated with sexually dimorphic adipocytokine and C3a responses. Overall, PFAA exposures were associated with the novel combination of increased biomarkers of hepatocyte apoptosis and decreased serum TNFα. These data support previous findings from cohorts and experimental systems that PFAAs may cause liver injury while downregulated some aspects of the immune response. Further studies of PFAAs in NAFLD are warranted and should evaluate sex differences.

Keywords: Cytokeratin 18; Non-alcoholic fatty liver disease (NAFLD); Perfluoroalkyl acids (PFAAs); Perfluorooctanoic acid (PFOA); Tumor necrosis factor alpha (TNFα).

Figure 1.. Disease Biomarker Heat Map

A heat map of the normalized logarithm of expression levels of biomarkers is demonstrated in colors that reflect expression levels (green represents low expression levels, red represents high expression levels). A color legend showing the normalized expression is on the left. The Venn diagram located in the upper part of the figure represents the exploratory hierarchical clustering analysis for associations among biomarkers based on their similarity, with the relative distance shown on the left axis (the smaller the closer).

Figure 2.. Significance of Biomarker Concentration in the Final Model

Adjusted beta coefficients are provided for each exposure and disease biomarker. These are graphical representations of the multivariate analysis results given in Table 2 (Final Model). Note that the range of the Y-axis varies between figures.

Figure 3.. Significant Sex Differences in Biomarker Associations

Significant relationships from the Interaction Model (Table 2) are depicted graphically. These figures are made using the coefficients from each respective linear model. The outcome variable (e.g., PFHxS) is continuous and log transformed, and the disease biomarker (e.g., adiponectin) is binary. One additional interaction was also statistically significant (PFOA and PAI-1) but is not displayed due to its small interaction coefficient estimate.